RB26 camshafts in RB20??

[Mr GTS4]

oh were art thou sk?? lol

[Turbine]

It kind of makes sense Mr GTS4 about moving the cam lobes further apart. But without trying it I wont know unless SK has any thoughts on it.

[Mr GTS4]

to me it is confussing so thats why i ask the people who do know. well installing adjustable cam gears aswell, would it make the car idle better (smoother)?? don't want to go buy them and then they don't work

[Warpspeed]

Well, I have never tried to fit an RB26 cam to an RB20, but I have a pretty fair idea of why you guys are having so many problems, so here goes:

First thing is that there will be a production variation between the sizes of the cam bearings. Not much, but then the bearing clearance is not much either, maybe a couple of thou. You cannot just swap cams without checking the bearing clearances. Well you can, but it is NOT a very good idea. You will never notice a sloppy bearing, but a tight one is going to be a real drama. So buy some plastigauge from Repco and measure the clearance of each cam journal with each cap properly torqued down.

The extra lift is so small it is hardly likely to bind the coils, but check it anyway. Turn the cam so each lobe is at maximum lift, and see how much further you can push down the follower. You should be able to get a 2mm gap at least before the valve spring goes solid. If not, you risk serious engine damage.

The cam drive gears ARE different between Skylines, so you cannot just bolt any old gears onto your cam and expect to get the exact factory timing. If in doubt get some adjustable cam gears, and take the time to set them up to Sydneykids figures.

The next problem is what has really defeated you guys and why your cars will not idle.

A hydraulic cam has no tappet clearance ramps. The base circle of the cam is flat, then the valve opens instantly at the specified opening point. Likewise it closes pretty suddenly back down to the base circle. Because the hydraulic lifters take up all the clearance, there will be no tappet noises.

A solid lifter cam is VERY different. From the flat base circle, there is a very shallow clearance ramp that begins very early and SLOWLY closes up the tappet clearance. Once the clearance has been taken up, the valve really starts to lift quickly. Likewise the valve drops fairly fast with the tappet clearance still all taken up, and there is an exit ramp that slowly opens up the tappet clearance.

These starting and ending ramps are very long, but only amount to perhaps half a millimeter of cam lobe lift.

If you fit a solid lifter cam like the GTR cam to a hydraulic lifter, like in an RB20, the valve timing at the beginning and ending is changed radically.

The hydraulic lifter goes solid, and the valve starts lifting off it's seat very early, much earlier than it should. The initial valve lift is extremely low, but the valve will still leak. Likewise during valve closing the valve is held just off its seat for an extended time.

What this means is that during engine idle, both valves will be open together for quite an extended time, but only just open. At 7,000 Rpm there is not enough time for any serious leakage. But at idle Rpm the valves will leak badly, because of the very large valve overlap this leak creates. It will sound fairly lumpy at idle, assuming you can actually get it to idle. A lumpy idle may sound really cool to some people.

Now the problem is, that at idle there is a fairly high vacuum in the inlet plenum. If both the inlet and exhaust valve are open together, exhaust will be sucked a fair way back up each intake runner. This exhaust will be drawn back into the engine causing the lumpy idle. The air fuel ratios will need some fairly drastic changes too from what they originally were. So don't expect it to work too well with a standard ECU. Even with a Power FC it will probably be quite difficult, if not impossible to get a smooth idle. I have never done this modification to an RB20, so I don't know how difficult it would actually be.

Your best bet might be to either go back to a proper hydraulic aftermarket cam, or fit the GTR solid lifters. I don't even know if that is possible on an RB20 head.

It is quite possible that a few guys have done this modification, and really like the rough idle, and say it makes the car sound mean. It probably also goes better at higher Rpm. Myself I prefer to have things working properly, and am not surprised some of you cannot get the engine to idle at all.

I wish you guys luck, but really what you are doing is not a terribly good idea unless the whole thing is approached properly.

[Jago]

yea i pm'd SK, he said best bet would be to do a solid lifter conversion, if you know what you are doing to do it yourself, otherwise go for an aftermarket RB20 set.

[DRIFTER]

do gtr lifters fit?

[floody]

Any ideas as to whether the advice applicable to R32 RB20's here re the cams is applicable to the HR31 redtop RB20s?

The redtop seems to have marginally more agressive cams from the factory*, but most aftermarket sites seem to list them as the same fitment for upgrades. But given the belt, gears etc are the same I'm hoping what goes for one goes for the other.

So a little different, but my guess is they should swap the same?

*Redtop is duration 248 in, 240 ex, 7.80 lift (both), LCA in 108, LCA ex 118.

*Silvertop is duration 240 in, 232 ex, 7.80 lift in, 7.30 lift ex, LCA in 111, LCA ex 118.

Edited November 9, 2006 by floody

[Adriano]

r32 rb20's havethe same problem, no power under 4000rpm if you fit gtr cams

[DVS JEZ]

r32 rb20's havethe same problem, no power under 4000rpm if you fit gtr cams

any one got a final verdict on this yet, bout to do fit my old GTR cams into a mates rb20 today hopefully, but only if it will work.

[mr_rbman]

any one got a final verdict on this yet, bout to do fit my old GTR cams into a mates rb20 today hopefully, but only if it will work.

pretty sure wazr32gtst is the only one to have success and sk. I'm going to fit some GTR cams to my rb25de head but get them welded and reground first!

[r3240sx]

I'm just curious as to where you guys find the drop in aftermarket cams for a good price... earlier in this thread people seem to think the GTR cams were almost not worth it when you can buy aftermarket for really cheap.

What is your idea of really cheap, I have not seen these cams for a reasonable price unless they're used.

Then again, I am in the states.

Good info guys!

[DJRIFT]

can anyone realy answer if this mod is clean cut a good idea, good power with minamal efort or is ait a good mod good power with a fair bit of stuffing around.

[r3240sx]

Well I went ahead and risked it, I have a set of GTR cams on order..

I'll report here when I get them in. Perhaps a dyno graph if time allows.

[DVS JEZ]

how much did you pay for them?

you could have looked in the for sale section and picked up a set for a bargain (from me)

[r3240sx]

I got them from a guy on nico. How much were you selling yours for?

I paid $175 USD shipped. A few people told me that was a good deal. If shipping isnt too bad my roommate might be interested in your cams. We're in the states btw.

[DVS JEZ]

pm sent

[r3240sx]

To take the head off and instalibng the cams isnt a real drama, doing it with the head in place holds a few challenges which means i may not be able to do it myslef...

plus with my new accomodationin i no longer have a suitable place to work on my car. The compression test on my engine next week, and a few things falling into place the next 24hrs will play a big role in whether i bother with my current engine, or start with a blank canvas.

I got my cams in the mail today.

I'll be installing them in about 5 minutes... just going to skim over this thread one more time, lol!

What should I do about tuning? I have an SAFC, and its corrected to about 12:1 when I ran 13 psi. I'm running 10 psi now.. Should I set the fuel correction to 0% just for safety until I can get my car on a dyno? I am at over -10% correction right now for most of the rev range.

Any input on my SAFC settings would be greatly appreciated.. also any tips on installation of these cams will probably help!

Thanks,

-Max

[TurboX]

Probably worth a search on "SK RB26 Cams into RB20"

From my experience make sure you lay the cams into the bearings in the exact correct orientation at Crank TDC with the cam gears aligned with the correct dot points. This will ensure you dont pull the cams down with the valves NOT HITTING the pistons.

Seems obvious I know but we nearly made the mistake first time.

Done it heaps now with Turbine and we always put the cams in without the belts first up so we can see they turn some way around (without hitting pistons) by hand fairly? freely without being bound tight.

We actually turned a few of the bearing tops aroud the other way to free up some journals so not binding.

Also may be worth soaking the bearing bolts for a few hours with crc before trying to remove them as sometimes they seem to bind up and you dont want to break them.

Good Luck and as i said:- "search"

[r3240sx]

Probably worth a search on "SK RB26 Cams into RB20"

From my experience make sure you lay the cams into the bearings in the exact correct orientation at Crank TDC with the cam gears aligned with the correct dot points. This will ensure you dont pull the cams down with the valves NOT HITTING the pistons.

Seems obvious I know but we nearly made the mistake first time.

Done it heaps now with Turbine and we always put the cams in without the belts first up so we can see they turn some way around (without hitting pistons) by hand fairly? freely without being bound tight.

We actually turned a few of the bearing tops aroud the other way to free up some journals so not binding.

Also may be worth soaking the bearing bolts for a few hours with crc before trying to remove them as sometimes they seem to bind up and you dont want to break them.

Good Luck and as i said:- "search"

Got the rb20 cams out.

The only problem I had was the bolts seizing in the cam caps.. I didnt break any bolts, but they sure dont turn well in the caps. I'll remove them from the caps tomorrow at work and find away to make them turn easily in the caps so they do not bind or break. Other than that, everything came off pretty easily, just marked the crap out of everything with a sharpie so that it will go back on properly...

I'll keep you guys posted, if I get the new seals and the bolts turning freely in the cam caps I'll have it back together by tomorrow night. Its about 15 degrees farenheit here right now and the roads are all iced over, so a butt dyno probably will not be very accurate... And Im not sure when I'll be able to get my car on the rollers... But I'll keep you posted on the change in exhaust note!

-Max

[Cubes]

I've been told by the bloke who worked on my head that upon removing the cams you must bleed the lifters as they can pump up slightly.

If the lifters have pumped up slightly and you install new cams it will cause the valve to open slightly and possibly kiss the piston resulting in a stuffed valve.

On that note, he didn't mention it BUT I have read here and there that to get around this problem some have spun their motors 10degree's off TDC, installed the cams and its all been good.

So becareful.

Those interested...

I think the cheapest way out of an aftermarket set of cams is to grab a set of GTR cams, send them off to LukeVL (from calaisturbo.com who works for or owns, Tighe Cams in QLD) and have them reground to your requirements.